The invention relates to a thermochromic polymerizable mesogenic composition comprising:
a) a component MA comprising at least one achiral polymerizable mesogenic compound comprising at least one polymerizable functional group, PA1 b) a component MB comprising at least one chiral polymerizable mesogenic compound comprising at least one polymerizable functional group, PA1 c) a photoinitiator, and PA1 d) optionally a dye component. PA1 a) a component MA comprising at least one achiral polymerizable mesogenic compound comprising at least one polymerizable functional group, PA1 b) a component MB comprising at least one chiral polymerizable mesogenic compound comprising at least one polymerizable functional group, PA1 c) a photoinitiator, and PA1 d) optionally a dye component. PA1 P is CH.sub.2.dbd.CW--COO--, WCH.dbd.CH--O--, ##STR1## PA1 or CH.sub.2.dbd.CH-phenyl-(O).sub.k -- with W being H, CH.sub.3 or Cl and k being 0 or 1, PA1 Sp is a spacer group having 1 to 20 C atoms, PA1 X is a group selected from --O--, --S--, --CO--, --COO--, --OCO--, --OCO--O--, --S--CO--, --CO--S-- or a single bond, PA1 n is 0 or 1, PA1 MG is a mesogenic or mesogenity supporting group preferably selected from formula II EQU --(A.sup.1 --Z.sup.1).sub.m --A.sup.2 -- II PA1 wherein PA1 R is an achiral alkyl radical with up to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen (up to perhalo) or CN (e.g., up to 4 times), it being also possible for one or more non-adjacent CH.sub.2 groups to be replaced, in each case independently from one another, by --O--, --S--, --NH--, --N(CH.sub.3)--, --CO--, --COO--, --OCO--, --OCO--O--, --S--CO--, --S--CO-- or --C.ident.--O-- in such a manner that oxygen atoms are not linked directly to one another, or alternatively R is halogen, cyano or has independently one of the meanings given for P--(Sp--X).sub.n --. The chiral polymerizable compounds of component MB are preferably selected from formula III EQU P--(Sp--X).sub.n --MG*--R* III PA1 P, Sp, X and n have the meanings given for formula I, PA1 MG* is a mesogenic or mesogenity supporting group, which is preferably selected from formula II given above, and PA1 R* is H or an alkyl radical with up to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen (e.g., up to perhalo) or CN (e.g., up to 4 times), it being also possible for one or more non-adjacent CH.sub.2 groups to be replaced, in each case independently from one another, by --O--, --S--, --NH--, --N(CH.sub.3)--, --CO--, --COO--, --OCO--, --OCO--O--, --S--CO--, --S--CO-- or --C.ident.C-- in such a manner that oxygen atoms are not linked directly to one another, or alternatively R* is halogen, cyano or has independently one of the meanings given for P--(Sp--X).sub.n --, PA1 A) coating a thermochromic polymerizable mesogenic composition comprising: PA1 B) aligning the polymerizable mesogenic mixture so that the axis of the molecular helix extends transversely to the layer; PA1 C) heating at least a part of the aligned mixture to a defined temperature, PA1 D) polymerizing at least a part of the aligned mixture by exposure to actinic radiation, PA1 E) optionally repeating, at least one more time, (D) alone or in combination with (C) or (A), (B) and (C), and PA1 F) optionally removing the substrate or, if present, one or two of the substrates from the polymerized material. PA1 X.sup.1 has the meaning given for X, PA1 Q.sup.1 is an alkylene or alkylene-oxy group with 1 to 10 C atoms or a single bond, PA1 Q.sup.2 is an alkyl or alkoxy group with 1 to 10 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH.sub.2 groups to be replaced, in each case independently from one another, by --C.ident.C--, --O--, --S--, --NH--, --N(CH.sub.3)--, --CO--, --COO--, --OCO--, --OCO--O--, --S--CO-- or --S--CO-- in such a manner that oxygen atoms are not linked directly to one another, or alternatively has the meaning given for P--Sp--, PA1 Q.sup.3 is halogen, a cyano group or an alkyl or alkoxy group with 1 to 4 C atoms different from Q.sup.2. PA1 A.sup.1, A.sup.2 and Z.sup.1 have the meaning given in formula II, PA1 R has the meaning given in formula I, PA1 i and j are independently of each other 0, 1 or 2, PA1 G.sup.1 is a terminal chiral group such as for example a cholesteryl group, ##STR11## PA1 G.sup.2 is a bivalent chiral group, for example, a bivalent chiral sugar or sugar derivative or another bivalent chiral radical as disclosed, e.g., in WO 95/16007, especially preferably a group based on 1,4:3,6-dianhydro-D-sorbitol: ##STR12## PA1 Q.sup.1 and Q.sup.3 have the meanings given in formula IV, and PA1 Q.sup.4 is an alkylene or alkylene-oxy group with 1 to 10 C atoms or a single bond, being different from Q.sup.1. PA1 a1) 10 to 80% by weight of component MA1 comprising at least one achiral polymerizable mesogenic compound according to formula I having one polymerizable functional group, PA1 a2) 0 to 70% by weight of component MA2 comprising at least one achiral polymerizable mesogenic compound according to formula I having two or more polymerizable functional groups, PA1 b1) 10 to 95% by weight of component MB1 comprising at least one chiral polymerizable mesogenic compound according to formula III having one polymerizable functional group, PA1 b2) 0 to 30% by weight of component MB2 comprising at least one chiral polymerizable mesogenic compound according to formula III having two or more polymerizable functional groups, PA1 d) 0 to 20% by weight of a dye component. PA1 a1) 10 to 80%, preferably 15 to 65%, in particular 20 to 50% by weight of two or more achiral polymerizable mesogenic compounds of component MA1, PA1 a2) 1 to 70%, preferably 2 to 55%, in particular 4 to 40% by weight of at least one achiral polymerizable mesogenic compound of component MA2, PA1 b1) 10 to 95%, preferably 15 to 90%, in particular 20 to 80% by weight of two or more chiral polymerizable mesogenic compounds of component MB1, and further comprises component c) and optionally components b2) and d) in the concentration ranges as described above. PA1 A) coating a thernochromic polymerizable mesogenic composition as described above and below on a substrate or between two substrates in the form of a layer, PA1 B) aligning the polymerizable mesogenic composition so that the axis of the molecular helix extends transversely to the layer, PA1 C) heating at least a part of the aligned composition to a defined temperature, PA1 D) polymerizing at least a part of the aligned composition by exposure to actinic radiation, PA1 E) optionally repeating, at least one more time, (D) alone or in combination with (C) or (A), (B) and (C), and PA1 F) optionally removing the substrate or, if present, one or two of the substrates from the polymerized material.
The invention further relates to anisotropic polymers and polymer films with a chiral mesophase obtainable from said thermochromic polymerizable mesogenic composition and to the use of said thermochromic polymerizable mesogenic composition, of said anisotropic polymers and cholesteric polymer films for optical information storage, photomasks, decorative pigments, cosmetics, security applications, active and passive optical elements such as polarizers or optical retarders, color filters, scattering displays, adhesives or synthetic resins with anisotropic mechanical properties.
The term "mechanical properties" is used to distinguish from the electrooptical properties of these materials (like birefringence or dielectric anisotropy), and comprises, e.g., anisotropic material properties such as thermal expansion coefficient, shear modulus, response to external mechanical stress, etc.
Thermochromic compositions, i.e., compositions that show a change of color upon temperature variation, are known in prior art. Usually low molar mass liquid crystals exhibiting a chiral mesophase, like cholesteric liquid crystals (CLCs) are used in thermochromic compositions. These materials exhibit a helically twisted molecular structure and show selective reflection of a specific wavelength band of light, wherein the reflected wavelength maximum varies upon change of the temperature. Such thermochromic compositions are disclosed for example in WO 90/02161.
For many applications, such as the preparation of colored films that can be used as optical films, e.g., patterned color filters, photomasks or films for optical information storage, materials like CLCs are needed wherein the reflected wavelength band remains substantially constant over a wide temperature range.
A suitable material for these applications would be a polymerizable thermochromic composition, wherein the desired pitch length and thereby the waveband reflected from that composition could be easily selected by temperature variation and afterwards the molecular structure with the selected pitch be fixed by polymerization, so that the reflected wavelength remains stable over a wide temperature range.
The European Patent Application EP 0 661 287 A1discloses polymerizable liquid crystalline siloxanes that show thermochromic behavior and can be polymerized to give linear liquid crystalline polymers with mesogenic side chains.
However, linear polymers and in particular polymers comprising siloxane chains like those disclosed in EP 0 661 287 most often exhibit low glass transition temperatures and show only limited temperature stability. Upon heating of these polymers their optical properties often deteriorate.
Consequently, there has been a considerable demand for a thermochromic material that can be polymerized to give an anisotropic polymer or polymer film with a helical structure that exhibits a higher temperature stability and a reflection wavelength that remains substantially constant over a wide temperature range, and does not have the disadvantages of the materials of prior art as discussed above.